The Leibnizian Cosmological Argument is discussed in a rather quick manner by Craig in Reasonable Faith, and a version of it is criticized in Le Poidevin’s Arguing for Atheism. It is stated as follows in Reasonable Faith:
1) Anything that exists has an explanation of its existence, either in the necessity of its own nature or in an external cause.
2) If the universe has an explanation of its existence, that explanation is God
3) The universe exists.
4) Therefore, the universe has an explanation of its existence. (from 1,3)
5) Therefore, the explanation of the existence of the universe is God. (from 2,4)(Craig 106)
P1 is a “modest version” of the Principle of Sufficient Reason (PSR). Le Poidevin attacks this at several points in his book. He mentions that perhaps the atheist could maintain that the universe is a contingent fact which needs no cause because causality is a spatiotemporal concept. This seems quite plausible—and curiously Craig does not discuss this objection even while defending the Kalam Cosmological Argument. I see this as quite a damaging objection as it stands since it could be said that since the universe cannot be said to have a cause that it will not have an explanation of its existence. Two other objections to PSR are; necessary facts cannot explain contingent ones and that invoking God as a causal explanation is problematic. Necessary facts cannot explain contingent ones because causes change environments, because of a cause something occurs that would not otherwise occur. However if the cause is necessary then it must obtain, therefore it does not properly explain anything, since as the cause had to occur so did the effect. However Le Poidevin seems to make this inference that necessary facts cannot explain “the whole” to “necessary facts then cannot explain contingent ones”(pg 40). I am not sure if that is completely sound, however if one defines causal explanation as making sense of facts that could have not been the case. The other objection concerns God as an explanation; now the only way God could cause something to be would be by a held intention. But intentions are not necessary they are contingent (an intention could have not obtained, it does not have to be)! And if intentions are contingent then they have an explanation outside of themselves and this it appears would lead to an infinite regress. As the Le Poidevin mentions the atheist may ask “why did the creator have such intentions? If the theist insists that this is one contingent fact that we cannot explain further, then the original motivation for explaining the existence of the universe is underminded.” In response the theist could say that it is necessary for God to have intentions and it just so happened that God decided to create a universe. This seems tenable, though there would still be no explanation as to why the intention of creation obtained and therefore there would not be a good explanation as to why there is something instead of nothing. Then perhaps the theist could deny the contingency of intentions, intentions for God could be a necessary consequence of his nature. This seems however to be very counter-intuitive and would deny libertarian freedom for God. It would seem then that there are two good objections to PSR, that the universe is a contingent fact that cannot be explained further and then that a personal explanation does not do for this argument.
P2 is rather straight forward, and I think Le Poidevin would accept it. However atheists like Quentin Smith would disagree and argue that P2 is completely false. (I will probably post more on his arguments later)
P3 is quite nice!
Another line one could take against this argument is that the universe exists necessarily. This is a common objection—though Le Poidevin denies it. Because of this I will not ponder on that objections for too long, only comment on how William Lane Craig denies it. Craig appears to believe that since it is quite conceivable that not the entire universe is necessary it must be contingent. This appears to be rather odd (at this point the discussion could return to intentionality and its contingency) since it is conceivable that God has different properties then he does(Omnimalevolence, impotence, or amorality to name a few), it does not follow that his existence could not be necessary. In the same way because the universe could have had different properties it does not follow that it in itself could not exist necessarily.
In conclusion then it appears that it is at least equally tenable that the existence of the universe is a contingent fact, compared with the contention that God is the reason for its existence. There are also some problems with God’s intentionality which might be worth exploring. Perhaps since it can be said that causality is a spatiotemporal notion it may be more plausible to deny then to accept PSR.
Craig, William L. Reasonable Faith: Christian Truth and Apologetics. 3rd ed. Vol. 1. Wheaton, IL: Crossway Books, 2088. N. pag. 1 vols. Print.
Le Poidevin, Robin. Arguing for Atheism: An Introduction to the Philosophy of Religion. London: Routledge, 1996. N. pag. Print.